Molding Materials Defects Solutions
The use of injection molding material can be difficult. Different materials must be selected for each job and the tooling used to ensure that quality parts are created. Sadly, due to the multitude of materials and their various behaviors when heated and then injected, there are always the potential for problems to arise. Here are some common defects and solutions for them.
Air Voids: Air voids result from air entrapment within the injected material, usually due to inadequate venting of the tool. To solve this, the tool should be checked to ensure that all vents are open and free of obstructions. If the vents are not cutting deep enough, they should be modified.
Weld Lines: Weld lines happen when two streams of injected material meet in one area, usually resulting in a weak spot on the part. To avoid this, the gate position should be changed so that the streams of material meet in a single location. If this is not possible due to design, then a vent should be added to the tool.
Flash: Flash occurs when the injected material escapes from the parting line and creates a thin, visible line along the edge. To fix this, the tool should be adjusted so that there is an adequate gap between the two parts and that the molding pressure is not too high. If this does not resolve the issue, then a backup feature should be added to the tool.
Burns: Burns are caused by overheated plastic, which can occur with fast molding cycles and thin wall sections. To fix this issue, the molding cycle should be slowed down and the temperature of the plastic should be reduced. If needed, additional cooling can be added to the tool to ensure the part is not overheated.
Shrinkage: Shrinkage occurs when the plastic cools and retracts after injection. To combat this, the tool design must account for this shrinkage. This can be done by adding cavities or ribs to the part, or by ensuring that the plastic material has a low shrinkage rate.
Warping: Warping is a common issue when parts being molded have large flat surfaces. To prevent this from happening, the part should be designed to ensure proper flow of the plastic material as it cools and retracts. Additional cooling may be required to help ensure the part remains flat and even.
These are just a few of the common defects that can occur during injection molding and the solutions to fix them. The key to successfully molding quality parts is to properly analyze and understand the material and the tool, and then make any necessary modifications. With careful consideration and the right modifications, these defects can be avoided and quality parts can be produced.
